At present, various conventional disk type mechanical combination locks are widely used in safes, file cabinets, security doors, vaults and warehouse doors.
FIGS. 1, 1A, 1B, 1C and 1D show a conventional disk type mechanical combination lock. As shown in FIG. 1A, a conventional disk type mechanical combination lock typically comprises 3–4 discs having a notch. The disc 1 is connected to a dial 5-0 outside the door by a spindle 5-1 and rotates synchronously with the dial 5-0. The discs 2 and 3 are fitted over a fixed sleeve (not shown) which is coaxial with the spindle 5-1. The discs 2 and 3 may either rotate or are immovable on the sleeve.
As shown in FIG. 1B, a control piece 6 is moved downwards and enters into the notches when all the notches 1-4, 2-4 and 3-4 of the discs 1, 2 and 3 are in alignment with the control piece 6. Restriction applied by the control piece 6 to the unlatching (unlocking) mechanism is released by the downward movement of the control piece 6, thus the latch will be released by the unlatching mechanism. However, even if only one notch is not in alignment with the control piece 6, the latch will not be released because the control piece 6 is prevented from moving downwards.
The process of inputting combination code is to align the notches of the discs with the control piece 6 by rotating the discs. The operation of inputting combination code is described as follows. As shown in FIG. 1C, the dial 5-0 outside the door is rotated in one direction (assuming in a counterclockwise direction) for at least three revolutions, then the disc 1 is certainly rotated synchronously. The disc 1 is dialed to rotate along with the dial 5-0 when a protrusive tongue 1-3 of the disc 1 is brought into contact with a protrusive tongue 2-3 of the disc 2, and the disc 2 is also dialed to rotate along with the dial 5-0 when the other end of the protrusive tongue 2-3 is brought into contact with a protrusive tongue 3-3 of the disc 3. The counterclockwise rotation of the dial 5-0 is stopped when the notch 3-4 of the disc 3 is in alignment with the control piece 6, the code on the scale plate of the dial 5-0 which is in alignment with a reference line is determined as the first combination code. As a result, the operation of inputting of the first combination code is completed.
As shown in FIG. 1D, when the dial 5-0 is rotated in the reverse direction (that is, in a clockwise direction) for almost one revolution, the protrusive tongue 1-3 of the disc 1 is brought into contact with the protrusive tongue 2-3 of the disc 2 from the other direction, and then the disc 2 is dialed to rotate along with the dial 5-0 synchronously in the clockwise direction. The clockwise rotation of the dial 5-0 is stopped when the notch 2-4 of the disc 2 is in alignment with the control piece 6, the code on the scale plate of the dial 5-0 which is in alignment with the reference line is determined as the second combination code. The operation of inputting of the second combination code is thus completed. Finally, the dial 5-0 is rotated in the counterclockwise direction for less than one revolution to ensure that the protrusive tongues 1-3 and 2-3 will not collide with each other, then the notch 1-4 of the disc 1 is also in alignment with the control piece 6. The whole process for inputting the combination code is thus finished. It should also be noted that whether protrusive tongues of discs are in alignment with the control piece 6 or not can not be acknowledged by a person outside the door, thus the above process is definitely under control of the scale on the edge of the dial 5-0 and a predetermined combination code. The position of the protrusive tongue 1-3 at the circumference of the disc 1 may be changed to alter the combination code, but only a few sets of combination code may be created.
As described above, the operation process for this kind of combination lock is very complicated. The operation will be even more complicated if the lock employs more discs. In order to reduce the number of the discs while increasing the number of the combination codes, the scale at the edge of the dial should be made very fine, which in turn requires a careful operation.
The conventional disk type mechanical combination lock described above has the following disadvantages:
1. The conventional disk type mechanical combination lock requires complicated operations. Since the outer dial is only connected to one driving disc at the inner side of the lock, thus other inner driven discs are not directly rotated by the dial, but indirectly driven through the collision between the respective protrusive tongues of the driving and driven discs. Therefore, in order to rotate these discs to a predetermined position, the dial is required to be rotated repeatedly in a forward direction and then in a reverse direction. For a conventional disk type mechanical combination lock with three discs, the forward and reverse rotation should be repeated for almost ten revolutions in order that a right combination code is dialed. If an advanced disk type mechanical combination lock in which dialing and unlocking is performed through the same dial is used, such as the those produced by Sargent & Greenleaf and LA GARD companies, the operation will be more complicated because an additional disc is introduced.
2. It is not easy to input the combination code in the conventional disk type mechanical combination lock. Because the combination code is recognized based on the fine scale at the edge of the dial and identified by use of a fine rotation angle, it has a great risk that the code is wrongly inputted due to a careless operation.
3. The conventional disk type mechanical combination lock has small quantity of combination codes. Taking a three-disc mechanical combination lock as an example, if the dial has 100 scale values, the lock will have 1003=1 million sets of combination codes in theory. However, such a number of codes can not be actually achieved at all. This is because it is very difficult to distinguish one scale value (3.6 degrees) by manual operation when the code is inputted by the dial. In addition, it is impossible to match the combination code according to one scale value due to machining errors generated in the manufacturing process. Adequate allowance have to be set in advance for the lock when it is manufactured so as to ensure that the combination code can be inputted successfully. Accordingly, the conventional disk type mechanical combination lock allows for ±1.5 difference in scale value, that is, every three scale values form one effective scale value. The finest scale at the edge of the dial will have 100 scale values, which forms 50 effective scale values. Therefore, a three-disc mechanical combination lock actually only have 503=125 thousand sets of combination codes, which is far less than the nominal code amount. The operation will become extremely complicated if a four-disc combination lock is adopted for purpose of increasing code amount.